Abstract
A 70-kDa lens membrane polypeptide (MP70) is a specific component of the fiber gap junctions. The C-terminal portion of MP70 is removed by age-related proteolytic processing, leaving an N-terminal 38-kDa polypeptide (MP38) in the membrane. Membrane association and topology of MP70 and of its processed form MP38 have been studied by hydrophobic labeling with 3-(trifluoromethyl)-3-(m-[125I]iodophenyl)diazirine and phenyl isothio[14C]cyanate. Membrane-embedded segments have been identified. They are localized in the N-terminal 30-kDa portion of MP70 and MP38. The C-terminal 40-kDa portion of MP70 appears to be exposed entirely at the cytoplasmic side of the junctional membranes. Hence, potentially poreforming peptide segments in the MP70 molecule are conserved upon age-related processing to MP38.
Highlights
From the *Department of Cellular & Molecular Biology, Centre for Gene Technology, University of Auckland, Auckland, New
Membrane association and topology of MP70 and of its processed form MP38 have been studied by hydrophobic labeling with 3-(trifluoromethyl)-3-(m-[12BI]iodophenyl) diazirine and phenyl isothio[“C]cyanate
The N-terminal amino acid sequence of MP70 is homologous to those of other gap junction polypeptides which belong to the family of connexins (Beyer et al, 1987; Kistler et al, 1988; Zhang and Nicholson, 1989)
Summary
From the *Department of Cellular & Molecular Biology, Centre for Gene Technology, University of Auckland, Auckland, New. A 70-kDa lens membrane protein (MP70) has been identified as a component of the fiber gap junctions (Kistler and Bullivant, 1989). MP70 is a component of the gap junctions in young fiber cells in the lens outer cortex and is cleaved to 38,000 (MP38) in the older cells located in the central region of the lens (Kistler and Bullivant, 1987). This age related processing is so far unique among gap junction proteins.
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